Rhabdoid tumors are lethal cancers that predominantly strike young children. The vast majority of rhabdoid tumors contain bi-allelic inactivating mutations in the SMARCB1 gene (see Roberts & Biegel, 2009, Cancer Biol. Ther. 8(5), 412-416).
Rhabdoid tumors are highly malignant neoplasms that typically arise in infancy and early childhood. The tumors develop in the brain and spinal cord [referred to as atypical teratoid/rhabdoid tumor (AT/RT)], kidney and/or soft tissues (termed malignant rhabdoid tumor or extra-renal rhabdoid tumor). The histologic appearance of these malignancies can be quite variable. Most tumors contain at least some fields with classic rhabdoid cells, with large nuclei containing a single prominent nucleolus, and cytoplasm with distinct pale eosinophilic inclusions. Tumors demonstrating only classic rhabdoid cells are rare, instead, they often have areas composed of spindled or pleomorphic undifferentiated cells without a rhabdoid phenotype. A classic rhabdoid component may be entirely absent. Central nervous system AT/RTs typically demonstrate a variety of primitive neuroectodermal, epithelial or mesenchymal cells, which underlies the difficulty in distinguishing these tumors from other primitive neuroectodermal tumors or choroid plexus carcinomas. Immunohistochemistry is often used in the differential diagnosis, based on the typical expression of smooth muscle actin, epithelial membrane antigen and vimentin. Lack of expression of the SMARCB1 protein is also employed as a specific means of distinguishing rhabdoid tumors from other malignancies with similar histologic features, especially for diagnosis of AT/RT versus primitive neuroectodermal tumors.
Individuals with germline alterations of SMARCB1 are predisposed to rhabdoid tumors of the brain, kidney and soft tissues and may present with more than one primary tumor. These children are most often diagnosed within the first year of life and tend to have a worse prognosis. It is not known whether the poor prognosis is related to the presence of a germline mutation in all of their cells, or the fact that they develop multiple and progressive primary tumors that are resistant to therapy.
The name SMARCB1 (SWI/SNF related, Matrix associated, Actin dependent Regulator of Chromatin, subfamily B, member 1) is derived from its role as a core member of the SWI/SNF chromatin remodeling complex. SMARCB1 is a core subunit present in all variants of the SWI/SNF complex. The protein is highly conserved, as evidenced by an identical amino acid sequence in mice and humans. However, the function of SMARCB1 is poorly understood. There are no SMARCB1 paralogs and the protein lacks particularly informative protein motifs.
The present invention seeks to provide novel therapies for the treatment of cancers such as rhabdoid tumors, as well as methods of selecting an effective treatment regime in cancer patients.